The ’70s Tony Award-winning musical “The Wiz,” a soulful retelling of L. Frank Baum’s “The Wonderful Wizard of Oz,” is back on Broadway. Contributor Kelefa Sanneh talks with members of the cast (including Wayne Brady, who is stepping into the shoes of the Wiz), and with director Schele Williams and writer Amber Ruffin, who are revising the show for today’s audience.